This invention relates to viewing devices in general, and more particularly to a cover plate associated with a carrier in which a micro-image transparency is mounted for viewing within the reader. Hereinafter, a transparency carrying a plurality of micro-images will be referred to as a microform.
In general, microform readers of the type to which this invention applies include a microform carrier incorporating a cover plate for holding a microform in the carrier, the assembly of the carrier and the microform being movable relative to the projection lens assembly in order to bring a selected micro-image into alignment with the projection lens assembly for the purpose of displaying the desired image. The cover plate is liftable relative to a microform support portion of the carrier in order to enable a microform to be inserted into, or removed from, the carrier.
In a known microform reader of the kind specified, the cover plate is pivotably connected to the microform support portion of the carrier by means of a pivot rod, and the projection lens assembly is urged by means of a spring into contact with the upper surface of the cover plate, the arrangement being such that, in order to lift the cover plate, the carrier is moved forwardly relative to the projection lens assembly until the carrier reaches a point at which the projection lens assembly is behind the pivot rod, whereupon the cover plate is pivoted upwardly to an open position under the action of the spring biased projection lens assembly.
This known microform reader has certain disadvantages. For example, the pivotal opening movement of the cover plate is a sudden movement and is therefore noisy. Further, each time the microform carrier is moved to a forward position to lift the cover plate, the position of the projection lens assembly is disturbed, thereby tending to give rise to focusing problems. Moreover, with the carrier in its forwardmost position, there is a risk of the cover plate being broken due to accidental depression thereof, since such depression of the cover plate is against the weight of the projection lens assembly.